Today we spend time to repair the VT-VFG of Bea-5. We did get assistance from Jo Scherpenisse, technician, and former colleague of the EWP, who designed a lot of modules, still in use in the Analog studio.

The VT-VFG did have problems with the manual (switch) shift input and the external shift input. When using the manual shit input (by pressing a button), the electronics sometimes skipped some steps. Very annoying for the users and it needed to be fixed.

We solved the ‘skipping steps’ problem by inserting a Maxim6816 chip in combination with a schmitt-trigger (CD4093) circuit with a small RC network. The Maxim6816 chip is a 'cmos switch debouncer’. By connecting a switch to this chip, the signal of the switch will be made ‘clean', so it’s better to be interfaced with digital electronics.

For the external shift input we inserted a schmitt-trigger (4093) with a resistor and a capacitor connected to the input. This circuit removes ‘unwanted spikes' from the external signal. Both circuits were placed on a small printed circuit board and inserted into the VT-VFG. The modification seems to work fine.

If you have acces to Bea-5 and you know how to work the VT-VFG, give it a try. If you do not know (yet) how it works,  you can also check the complete manual of Bea-5 here.

2015-03-05 21:58:54
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